Method to limit temperature increase in a catalyst and detect a restricted exhaust path in a vehicle

ABSTRACT

A vehicle has an engine, an exhaust aftertreatment system, an electric machine, and a controller configured to, in response to an actual engine torque output being less than an inferred engine torque, shut down the engine. A vehicle has an engine, an exhaust aftertreatment system, an electric machine, and a controller configured to, in response to an actual engine torque output being less than a first threshold and a torque request to the engine being greater than a second threshold, set a diagnostic code. A method includes receiving an actual engine torque output, receiving an engine torque request, and shutting down the engine when the actual engine torque output is less than a first threshold and the engine torque request is greater than a second threshold for a predetermined time period to limit temperature increase of a catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 13/597,907filed Aug. 29, 2012, the disclosure of which is hereby incorporated inits entirety by reference herein.

TECHNICAL FIELD

Various embodiments relate to monitoring engine conditions to limit atemperature increase in a catalyst or to detect restricted airflow in anexhaust aftertreatment system in a vehicle, including a hybrid electricvehicle (HEV).

BACKGROUND

Vehicles with engines require engine exhaust aftertreatment systems toremove unwanted chemicals from the exhaust flow and meet emissionsrequirements. The engine exhaust aftertreatment system may be acatalytic converter. In the case of a three-way catalytic converter,various amounts of carbon monoxide, unburned hydrocarbons and nitrousoxides are removed from the engine exhaust flow before it exits thevehicle to the environment. Unburned hydrocarbons may include unburnedfuel and partially burned fuel. If high levels of unburned hydrocarbonsare permitted to reach the catalytic converter, the catalytic convertertemperature may increase due to chemical reactions between the unburnedhydrocarbons and oxygen caused by the catalyst material. These chemicalreactions release heat. The temperature rise in the catalytic convertermay lead to catalyst degradation or damage, with the potential forcatalyst meltdown, restricted exhaust flow, and catalyst deactivation.

Hybrid vehicles may have electric motors configured to rotate the enginewithout combustion occurring. This hybrid architecture may allow highlevels of unburned hydrocarbons reaching the catalytic converter if theelectric motor is rotating the engine while the engine is misfiring,stalling, or complete combustion is otherwise not occurring within acylinder.

A system and method needs to be provided to monitor the engine andexhaust to detect and/or prevent large amounts of unburned hydrocarbonsfrom reaching the catalytic converter, or to provide a diagnostic codewhen it does occur.

SUMMARY

In an embodiment, a vehicle is provided with an engine, an exhaustaftertreatment system having a catalyst, an electric machine, and atleast one controller. The at least one controller is configured to, inresponse to an actual engine torque output being less than an inferredengine torque output for a predetermined time period, shut down theengine to limit temperature increase of the catalyst.

In another embodiment, a vehicle is provided with an engine, an exhaustaftertreatment system, an electric machine, and at least one controller.The at least one controller is configured to, in response to an actualengine torque output being less than a first threshold and a torquerequest to the engine being greater than a second threshold for apredetermined time period, set a diagnostic code to indicate restrictedair flow in the aftertreatment system.

In yet another embodiment, a method for controlling an engine isprovided. Data indicative of an actual engine torque output is receivedfrom an electric machine configured to control the speed of the engine.Data indicative of an engine torque request is received. The engine isshut down when the actual engine torque output is less than a firstthreshold and the engine torque request is greater than a secondthreshold for a predetermined time period to limit temperature increaseof a catalyst in an engine aftertreatment system

Various embodiments according to the present disclosure have associatedadvantages. For example, torque may be used to determine whether theengine is operating or stalling/misfiring with unburned hydrocarbonsbeing motored to the catalytic converter to detect conditions that maydegrade or damage the catalyst and preserve the catalyst. Alternatively,the algorithm may detect conditions showing that the catalyst isdegraded or damaged, and an appropriate diagnostic code may be set for aservice technician. Detection may be difficult, as the vehicle maycontinue to meet emissions regulations as the flow over the remainingdegraded or damaged catalyst surface area is restricted. Previousmonitors were unable to operate unless the catalyst was inactive, couldnot diagnose low engine power complaints caused by restricted flowthrough the catalytic converter, and could not detect a throttle stuckin a closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hybrid vehicle capable ofimplementing various embodiments of the present disclosure;

FIG. 2 is a flowchart depicting an algorithm for detecting a stallcondition for a catalyst monitor according to an embodiment; and

FIG. 3 is a flowchart depicting an algorithm for detecting a partiallyblocked exhaust path from a damaged catalyst for a catalyst monitoraccording to an embodiment.

DETAILED DESCRIPTION

As required, detailed embodiments of the present disclosure aredisclosed herein; however, it is to be understood that the disclosedembodiments are merely exemplary and may be embodied in various andalternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the claimed subject matter.

In FIG. 1, an embodiment of a hybrid electric vehicle (HEV) is shownthat may be used with the diagnostic of the present disclosure. Ofcourse, FIG. 1 represents only one type of HEV architecture, and is notintended to be limiting. The present disclosure may be applied to anysuitable HEV. Furthermore, the present disclosure may be applied to anyconventional vehicle that includes a start motor or other device forrotating the crankshaft when the engine is not operating.

Engine 20 is a primary power source in the HEV configuration of FIG. 1.A secondary power source is a combination of a generator 40, an electricmotor 42, and a battery and battery control module 44. The components ofthe combination are electrically coupled by an electrical high voltagebus. In some embodiments, the battery 44 is additionally rechargeable ina plug-in hybrid electric vehicle (PHEV) configuration using areceptacle 45 connected to the battery 44, possibly through a batterycharger/converter unit. The receptacle 45 may be connected to the powergrid or other outside electrical power source to charge the battery 44.

The powertrain includes a transmission 46, which comprises a planetarygear unit 48, the generator 40 and the motor 42, as well as torquetransfer counter shaft gearing 50. The planetary gear unit 48 comprisesa ring gear, a sun gear, a planetary carrier and planet gears rotatablysupported on the planetary carrier for engagement with the ring gear andthe sun gear. A power output gear element of the gearing 50, isdriveably connected to a differential-and-axle assembly 52, whichdistributes power to vehicle traction wheels 54. In other embodiment,other transmission 46 architectures may be used as are known in the art.

An overall controller for the operating modes of the powertrain may beimplemented by a vehicle system controller (VSC) 56, electronic controlunit (ECU), or controller, that receives various inputs including driverinputs at 58 and 60. The input at 58 is an accelerator pedal positionsensor signal (APPS) and the input at 60 is driver selection for “park,”“reverse,” “neutral” or “drive range” (PRND).

The engine 20 has an exhaust 22, which flows through an aftertreatmentsystem 24 containing a catalyst, such as a catalytic converter or thelike, and to the environment. The catalytic converter 24 contains asubstrate which supports a catalyst material as is known in the art. Thecatalyst material chemically reacts with the exhaust to reduce emissionsof unburned hydrocarbons, carbon monoxide, and nitrous oxides.

If the engine 20 stalls, misfires or otherwise has incomplete combustionwhile being rotated, such as when being spun by the generator 40, anunburned fuel and air mixture flows through the exhaust 22 and to thecatalytic converter 24. The temperature in the catalytic converter 24can rise to the point where the catalyst may melt if the unburnedhydrocarbon level is sufficiently high and conditions in the catalyticconverter 24 and vehicle are met, i.e. high catalyst temperature.Additionally, if catalyst melting occurs in the catalytic converter 24,an increased back pressure on the engine 20 from exhaust flowrestriction may reduce the engine power output. Catalyst degradation,melting, or damage may undetectable using emissions sensors, as therestricted flow over the remaining catalyst material often meets vehicleemissions regulations.

A flow chart illustrating an embodiment of a diagnostic or monitor usingalgorithm 70 is shown in FIG. 2. The algorithm 70 may detect an enginestall based on actual engine torque, inferred engine torque, andrequested engine torque to detect and/or prevent conditions that maydamage the catalyst. The algorithm 70 may be implemented by the VSC 56and use sensor data available to the VSC 56. In one embodiment,algorithm 70 detects conditions that may lead to catalyst damage andoperates the vehicle to prevent damage.

The algorithm 70 starts at 72. The controller 56 determines if theengine 20 is being commanded to run or operate at 74. This does not meanthat the engine 20 is actually operating and combusting, for example,the engine 20 could be commanded to run but be stalled or misfiring, andnot operating correctly.

The algorithm 70 then determines if various entry conditions are met at76. For example, entry conditions may include the engine 20 not being insecondary idle where the engine is operating in speed control and atorque measurement would not be valid. Another entry condition is theengine 20 not operating in spark retard above a specified torque ratio,i.e. above 50%. Another entry condition is the engine 20 operatingwithout any fuel injectors being cut or disabled, such as when aninjector needs replacement, is above a specified temperature, or when anignition coil needs replacement. Another entry conditions is that theengine 20 is synchronized. When the engine 20 is unsynchronized, theengine 20 position is unknown and needs to be resynchronized, and theentry condition will not be met. All or some of these entry conditionsneed to be satisfied for algorithm 70 at 76, although the list is notinclusive and other entry conditions as are known in the art may berequired.

If the entry conditions are satisfied at 76, the algorithm 70 thendetermines the inferred torque produced by the engine 20 at 78. Theinferred torque is the amount of torque that the engine 20 is expectedto produce based on the operating conditions of the engine 20. Theinferred torque may be determined as is known in the art, for example asa function of the amount of fuel and air flowing into the engine 20, orusing an engine 20 map. The VSC 56 may use measurements from fuelsensors, air sensors, or other engine 20 sensors as required todetermine the inferred torque. In one embodiment, the controller 56 mapsthe inferred torque for the engine 20 from the air and fuel flowing tothe engine, the amount of spark retard commanded for the engine, and thespeed of the engine. Alternatively, the inferred torque may be availablefrom a controller area network (CAN) in communication with the VSC 56.

The algorithm 70 then determines a threshold, T1, from a calibrationtable at 80. The calibration table may provide the threshold, T1, as afunction of the inferred torque and the engine coolant temperature. Alower engine coolant temperature may desensitize T1.

The algorithm 70 then measures the actual torque produced by the engine20 at 82. In one embodiment, the actual engine torque output may bemapped using generator 40 current, generator 40 speed, and engine 20speed in the HEV as disclosed above. Other measurements may also be usedto map the actual engine torque output, such as the outer ring speed ofthe planetary gear unit 48. The actual engine torque output may also bemeasured using a torque sensor. Other vehicle sensors and vehiclecomponents may be used to determine the actual engine 20 torque outputbased on the system architecture. The actual engine torque output may beavailable from the CAN.

The algorithm 70 compares the actual torque produced by the engine 20 toT1 for a specified time at 84. For example, the time may be on the orderof one second and be a sustained time. In one embodiment, T1 is on theorder of approximately 25-30% of the inferred torque value, meaning thatthe actual torque output of the engine 20 is much less than what itshould be producing based on the inferred torque determined from theengine map. If the actual torque is greater than T1 at 84, the algorithm70 proceeds to 86 where it determines the requested torque. Therequested torque is the torque that the engine 20 is being commanded toproduce, and may be available from the CAN. The requested torque is setas the minimum of either the instantaneous (fast) torque or the longterm (slow) torque at 86. Fast torque is based on the spark path in theengine 20, and will be reduced for example using spark retard. Slowtorque is based on the air path in the engine 20, and will be reducedfor example by restricting the air flow.

At 88, the actual torque is compared to a second threshold, T2, and therequested torque from 86 is compared to a third threshold, T3, for aspecified time period. In an embodiment, the thresholds, T2, T3, are setvalues or constants. In one example, T2 is −1 Nm, T3 is 59 Nm, and thetime period is forty five seconds sustained. Of course, other values maybe used in other embodiments of the disclosure.

If the actual torque is less than T2 and the requested torque is greaterthan T3 for the specified time at 88, the algorithm 70 proceeds to 90.Alternatively, the algorithm 70 proceeds from 84 to 90 if the actualtorque is less than T1 at 84. At 90, the algorithm 70 increments a stallcounter based on one of four stall criteria. The stall criteria include:the engine starting while the catalyst is cold, the engine startingwhile the catalyst is hot, the engine stalling while the catalyst iscold, and the engine stalling while the catalyst is hot. Whether thecatalyst is hot or cold is based on a temperature measurement of thecatalyst and set temperature ranges for the catalyst. Each stallcriteria has a different maximum count value that is associated with thestall counter. For example, the starting cold criteria will have ahigher maximum stall count value than the starting hot criteria becausethe engine 20 may be restarted a larger number of times before unburnedhydrocarbons cause the catalytic converter to heat to the point wherethe catalyst may melt. In one embodiment, the stall criteria is based onthe catalyst temperature and the engine start condition, i.e. whetherthe engine was in a start sequence or had been operating for a time.

At 92, the stall counter is compared to the maximum count value for thatstall criteria. If the stall counter is greater than the maximum countvalue at 92, the algorithm 70 sets a diagnostic code at 94. Thealgorithm 70 may also cause the controller 56 to send a command to shutdown the engine 20 at this time in order to protect the catalyst frompotential damage. In some embodiments, the diagnostic code at 94 maycause the vehicle to enter a limited mode of operation, such as aservice mode, and may provide a service indicator to the user.

If the stall counter is less than the maximum count value at 92, theengine 20 is commanded to restart the combustion process while thevehicle is operating at 96, and the algorithm 70 then proceeds back to72.

Referring to 88, if the actual torque is greater than T2 and/or therequested torque is less than T3 for the specified time, the algorithm70 proceeds to 98. At 98, the algorithm 70 determines if a specifiedtime period has elapsed with no stalls. In one embodiment, the time isthirty seconds. If the specified time has elapsed with no stalls at 98,the stall counter is cleared at 100 and the algorithm 70 returns to 71.If the time has not elapsed without stalls at 98, the algorithm 70returns to 72.

FIG. 3 illustrates a flow chart of an embodiment of a diagnostic ormonitor using algorithm 110. The algorithm 110 may be used to detect azone where the engine 20 is operating between normaloperation/combustion and complete stall to detect and/or preventconditions that may degrade or damage the catalyst due to unburnedhydrocarbons. The algorithm 110 may be implemented by the VSC 56 inconjunction with or independent of algorithm 70 as shown in FIG. 2. Inone embodiment, algorithm 110 detects conditions that may confirmexisting catalyst degradation or damage where engine power output islimited due to a restricted exhaust flow. For steps similar to thoseshown in FIG. 2, refer to the discussion above with respect to FIG. 2.

The algorithm 110 starts at 112. The controller 56 determines if theengine 20 is being commanded to run or operate at 114. The algorithm 110then determines if various entry conditions are met at 116. For example,entry conditions may include the engine 20 not being in secondary idlesuch that the engine is operating in speed control and a torquemeasurement is not valid, the engine 20 not operating in spark retardabove a specified torque ratio, i.e. above 50%, the engine 20 operatingwithout any fuel injectors being cut or disabled, and that the engine issynchronized. All or some of these entry conditions need to be satisfiedfor algorithm 110 at 116, although the list is not inclusive and otherentry conditions as are known in the art may be required.

If the entry conditions are satisfied at 116, the algorithm 110 thendetermines the inferred torque produced by the engine 20 at 118.

The algorithm 70 then determines a threshold, T4, from a calibrationtable at 120. The threshold, T4, may be a function of the inferredtorque and the engine coolant temperature. The algorithm 110 thenmeasures the actual torque produced by the engine 20 at 122.

The algorithm 110 compares the actual torque produced by the engine 20to T4. If the actual torque is greater than T4 at 124, the algorithm 110proceeds to 126 where it determines the requested torque. The requestedtorque is the torque that the engine 20 is being commanded to produce.The requested torque is set as the minimum of either the instantaneous(fast) torque or the long term (slow) torque at 126.

At 128, the actual torque is compared to a threshold, T5, and therequested torque from 126 is compared to a threshold, T6. In anembodiment, the thresholds, T5, T6, may be set values or constants. Inone example, T5 is 5 Nm, −1 Nm, or −100 Nm, and T6 is 59 Nm. Of course,other values may be used in other embodiments.

If the actual torque is less than T5 and the requested torque is greaterthan T6 at 128, the algorithm 110 proceeds to 130. Alternatively, thealgorithm 110 proceeds from 124 to 130 if the actual torque is less thanT4 at 124. In one embodiment, T4 is on the order of approximately 50% ofthe inferred torque. At 130, the algorithm 110 increments a timer. At132, the timer is compared to a predetermined time value. In oneembodiment, the time value is forty five seconds. If the timer isgreater than the time value at 132, the algorithm 110 sets a diagnosticcode at 134. If the timer is less than the time value at 132, thealgorithm proceeds back to 112.

If the actual torque is greater than T5 and/or the requested torque isless than T6 for the specified time at 128, the algorithm 110 proceedsto 136. At 136, the algorithm 110 decrements or clears the timer, andthe algorithm 110 returns to 112.

Various embodiments according to the present disclosure have associatedadvantages. For example, torque may be used to determine whether theengine is operating or stalling/misfiring with unburned hydrocarbonsbeing motored to the catalytic converter. This allows for detection ofconditions that may degrade or damage the catalyst to preserve thecatalyst. Alternatively, the algorithm may detect conditions showingthat the catalyst is degraded or damaged, and an appropriate diagnosticcode may be set for a service technician. Detection may be difficult, asthe vehicle may continue to meet emissions regulations as flow over theremaining degraded or damaged catalyst surface area is restricted.Previous monitors were unable to operate unless the catalyst wasinactive, could not diagnose low engine power complaints caused byrestricted flow through the catalytic converter, and could not detect athrottle stuck in a closed position.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of that are not explicitlyillustrated or described. Where one or more embodiments have beendescribed as providing advantages or being preferred over otherembodiments and/or over prior art with respect to one or more desiredcharacteristics, one of ordinary skill in the art will recognize thatcompromises may be made among various features to achieve desired systemattributes, which may depend on the specific application orimplementation. These attributes include, but are not limited to: cost,strength, durability, life cycle cost, marketability, appearance,packaging, size, serviceability, weight, manufacturability, ease ofassembly, etc. As such, any embodiments described as being lessdesirable relative to other embodiments with respect to one or morecharacteristics are not outside the scope of the claimed subject matter.

1-10. (canceled)
 11. A vehicle comprising: an engine; an exhaustaftertreatment system having a catalyst; an electric machine; and acontroller configured to, in response to actual engine torque outputbeing less than a first threshold and requested engine torque beinggreater than a second threshold, set a diagnostic code indicatingrestricted air flow across the catalyst.
 12. The vehicle of claim 11wherein the controller is further configured to set the diagnostic codein response to actual engine torque output being less than an expectedengine torque output.
 13. The vehicle of claim 11 wherein the firstthreshold is less than the second threshold.
 14. The vehicle of claim 11wherein the controller is further configured to set requested enginetorque as the smaller of an instantaneous torque request and a long-termtorque request.
 15. The vehicle of claim 11 wherein the controller isfurther configured to set the diagnostic code in response to satisfyingan entry condition based on an engine state.
 16. The vehicle of claim 15wherein the entry condition is unsatisfied if one of unsynchronizedengine operation, spark retard above a predetermined level, a disabledfuel injector and operating in secondary idle is present. 17-20.(canceled)
 21. The vehicle of claim 11 wherein the first threshold isset as a constant value, and the second threshold is set as anotherconstant value.
 22. The vehicle of claim 11 wherein the controller isfurther configured to set the diagnostic code in response to actualengine torque output being less than a third threshold.
 23. The vehicleof claim 22 wherein the third threshold is a function of expected enginetorque output and an engine coolant temperature.
 24. The vehicle ofclaim 23 wherein the controller is further configured to set the thirdthreshold by inputting expected engine torque output and engine coolanttemperature into a calibration table.
 25. The vehicle of claim 12 thecontroller is further configured receive a signal from the electricmachine indicative of actual engine torque output.
 26. The vehicle ofclaim 12 wherein the controller is further configured to determineexpected engine torque output as a function of air flow, fuel flow,commanded spark retard, and engine speed.
 27. The vehicle of claim 11wherein the controller is further configured to increment a timer inresponse to actual engine torque output being less than the firstthreshold and the requested engine torque being greater than the secondthreshold, and set the diagnostic code indicating restricted air flowacross the catalyst when the timer reaches a predetermined time value.28. The vehicle of claim 27 wherein the controller is further configuredto decrement the timer in response to at least one of actual enginetorque output being greater than the first threshold and requestedengine torque being less than the second threshold.
 29. A vehiclecomprising: an engine; an electric machine; and a controller configuredto: (i) increment a timer if actual engine torque output (T) being is afirst threshold, (ii) increment the timer if τ is less than a secondthreshold and requested engine torque is greater than a third threshold,and (iii) set a diagnostic code indicating restricted air flow across anengine exhaust catalyst if the timer exceeds a predetermined value. 30.The vehicle of claim 29 wherein the first threshold is a function ofexpected engine torque output, and wherein the second and thirdthreshold are constants, the second threshold being less than the thirdthreshold.
 31. The vehicle of claim 29 wherein the controller is furtherconfigured to decrement the timer if at least one of T is greater thanthe second threshold and requested engine torque is less than a thirdthreshold.
 32. The vehicle of claim 29 wherein the controller is furtherconfigured to set requested engine torque request as the smaller of aninstantaneous torque request and a long-term torque request.
 33. Thevehicle of claim 29 wherein the controller is further configured toperform steps (i), (ii), and (iii) sequentially.
 34. The vehicle ofclaim 29 wherein the electric machine is configured to control a speedof the engine; and wherein the controller is further configured toreceive a signal indicative of actual engine torque from the electricmachine.